I'd ride the whole route if there are no constraints like time, money or fitness. Last October I rode from my home in Santa Rosa, California to the Mexican border in 14 days (I'm 69, so a bit slower); it was an awesome trip! If you are constrained to a shorter journey, I'd suggest riding from Astoria to San Francisco. I would advise against doing this until late May or early June as the Pacific Northwest is famous for rain. You don't say if you're planning to camp or stay in motels, Oregon has great hiker-biker campgrounds, but sadly, California has shut most of their H-B sites south of Ventura due to the homeless population taking them over. Have fun!
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